Animal Movements in Heterogeneous Habitats

Matthew Bramble – The Influence of Field Margins on Insect Distributions in Forage Crop Agroecosystems

The objective of this preliminary study was determine if field margins affect the distribution and abundance of insect pests and predators within a forage crop agroecosystem. We hypothesized that field margins with supplementary food resources would affect the density and distribution of insects within alfalfa fields. We predicted that specialist herbivores and their predators would have higher densities at the boundary between margins and alfalfa fields and non-specialist herbivores and their predators would have higher densities in field margins with the absence of legumes.  Using a Latin square design, three types of field margins with orchard grass, red clover or buckwheat were used to determine their effects on insect distributions within fields of alfalfa. Insects were sampled using sweep nets and D-Vac suction sampling to determine the densities of pests and spiders in field margins and interiors of the alfalfa fields. We found that the most abundant pests - leafhoppers- exhibited highest densities at the boundary between the margins and the alfalfa due to the spill-over of insects from red clover and buckwheat margin types.  In the treatment using only orchard grass, leafhoppers decreased in abundance with distance into the interiors of the alfalfa field. Grasshoppers also followed the same patterns as the leafhoppers. The most common predator, spiders, exhibited highest abundances in the margins containing red clover and orchard grass and also at greater distances into the alfalfa.  The predators had low abundance at the edges between margins and alfalfa. Spiders increased in abundance from the margin into the alfalfa in the treatment containing buckwheat.  We conclude that field margins have a strong influence on the distribution and abundance of arthropod pests and predators in forage crop agroecosystems.

Coral Navedo –Effects of Golf Course Pond Water and an Insecticide on Cricket Frog Tadpole Activity and Development

Habitat destruction and chemical pollution are major issues in amphibian conservation. It has been established that terrestrial buffer zones around wetlands protect aqueous habitats while helping filter chemical pollutants.  The golf course landscape may be an excellent possibility for combining recreation with habitat creation and species conservation.  However, heavy application of pesticides could have adverse effects on organisms that are unintentionally exposed to them such as the Northern Cricket Frog, which is declining throughout parts of its range.  We studied the effects on survival, development, and behavior of the Northern Cricket Frogs reared in golf course pond water from ponds with and without grass buffer zones.  We also exposed tadpoles to the presence or absence of a realistic field concentration of the insecticide imidacloprid, which is commonly used on golf courses.  We conducted a long-term study during which tadpoles were observed to measure survival for forty-eight days.  Mass and developmental stage were measured on the forty-eighth day of observation.  The effects of imidacloprid were studied in a 24-hour predator-prey experiment where we measured the activity level and survival of tadpoles. Water from different golf courses had different effects on survival; tadpoles reared in water from buffered ponds had higher survival then those reared in non-buffered pond water.  Tadpole activity was affected by different pond water; tadpoles from Oxford Country Club were significantly more active than tadpoles in other pond water.  The effect of imidacloprid on survival differed between all golf courses and was not significant.  Although not significant, tadpole mass also differed by golf course.  This study will help with conservation efforts for amphibians, helping with finding new potential habitats and understand their susceptibility to a widely used insecticide.

Haley Davis –Use of UV powder to assess the social monogamy of male prairie voles, Microtus ochrogaster

 Several laboratory studies have linked differences in the vasopressin receptor in male mammals to differences in the strength of their preference for a particular social partner. It has been shown that these differences in display of social monogamy may be connected to a single microsatellite at the 5’ regulatory region of the vasopressin 1a receptor. Prairie voles, one of the few mammals that are thought to be socially monogamous, have been the subject of many of the studies. Our objective was to determine if the number of females with which a male prairie vole interacts is related to the length of the microsatellite region of the vasopressin receptor gene. Based on laboratory studies, we expected that males with longer microsatellites would be more socially monogamous and come in contact with fewer females than males with shorter microsatellites. UV fluorescent powders were applied to the males and females were then examined to see if powder had been transferred to them, an indication of a social interaction. The location of the powder on the female was noted and used to determine if the interaction was likely to be sexual or not. Female nests were also examined for powder to see how many females’ homes each male had visited. Our results showed that there is no significant relationship between the length of the microsatellite and the number of females with which a male interacted. We also found no significant relationship between the allele length and the number of females’ burrows a male visited. This indicates that social monogamy may be influenced by more than just the vasopressin receptor.  Perhaps there is not just one “gene of monogamy” as it was previously thought. 

Julie Charbonnier – Influence of Pond Canopy Cover During Larval Development on Post-Metamorphic Dispersal Ability of a Toad (Bufo americanus)

Dispersal is an important process for animals with complex life cycles, such as pond-breeding amphibians. Following metamorphosis, juvenile amphibians must disperse from their natal ponds to suitable terrestrial habitats. The conditions of the larval pond environment (e.g., pond canopy cover) have been shown to influence various measures of metamorph performance including growth rate and survival. Conditions of the larval environment may similarly influence the ability of metamorphs to disperse to the terrestrial environment. Since dispersal is difficult to measure directly, measurements of locomotor performance may provide a good indication of potential dispersal ability for juvenile amphibians. We raised American toad (Bufo americanus) larvae in open- and closed-canopy pond mesocosms and retained 40 metamorphs from each pond type for locomotor performance trials.  We conducted speed and endurance trials on metamorphs to test the effects of pond canopy cover on juvenile locomotor ability. We also examined citrate synthase activity of hindlimb skeletal muscle to estimate the proportions of endurance and speed type muscle. Based on preliminary data, we anticipated a trade-off between speed and endurance with open-canopy toads having greater endurance and reduced speed. We found that toads from closed-canopy ponds were significantly larger and as a consequence had both higher absolute endurance and speed. However, after statistically removing the effect of body size, we found that toads from open-canopy ponds had higher relative endurance, which would facilitate the longer dispersal distance between open-canopy pond habitat and forested terrestrial habitat. Contrary to our prediction, we found that toads from open-canopy ponds had lower citrate synthase activity. Since citrate synthase activity did not account for the relatively higher endurance of open-canopy toads, our results suggest that another mechanism may underlie this differential performance. Moreover, our results suggest that since toads from closed-canopy ponds were larger at metamorphosis and had higher overall locomotor performance, which may lead to enhanced fitness, closed-canopy ponds may be better quality population sources and open-canopy ponds may be lower quality population sinks.